Stuff the box so it will not get crushed. One sheet of crumpled paper from your recycle bin works well. Clearly write the address above on your box and consider using colorful stamps to close the top and bottom. The stamp cancellations showing its origin will make it even more meaningful.
It's okay to put as many stamps as you want anywhere on your SOUL BOX as long as they add up to the postage due. If you have stuffed the box if will go through the postal system just fine.
When you bring people together to fold Soul Boxes, consider including a jar for donations. The money can be used to defray the cost of shipping Soul Boxes to our Portland workshop or buying materials. When asked, you'll find people are happy to help!